plugins/elements/live_bootstrap.py: Fix enum usage
File "freedesktop-sdk-binary-seed/plugins/elements/command.py", line 93, in assemble
self.extra_assemble(sandbox)
File "freedesktop-sdk-binary-seed/plugins/elements/live_bootstrap.py", line 90, in extra_assemble
if self._system == "sysa":
^^^^^^^^^^^^^^^^^^^^^^
File "buildstream/src/buildstream/types.py", line 70, in __eq__
raise ValueError("Unexpected comparison between {} and {}".format(self, repr(other)))
ValueError: Unexpected comparison between System.SYSA and 'sysa'
Fixup for !75 (merged)